1. Field of the Invention
The present invention relates to a torsion beam suspension, in detail, the construction of attachments to the wheels set to the both ends of the torsion beam extended to the vehicle width direction.
2. Related Art
Conventionally, some prior arts disclose some torsion beam suspensions, there is known various technology referring to the torsion beam suspension (for example, see JP-U-7-71883 and JP-A-62-299402).
The conventional torsion beam suspension is composed of a torsion beam and attachments to a body, disclosed JP-U-7-71883 and JP-A-62-299402. The torsion beam is constructed as a single pipe, which includes a cross portion and an arm, and the cross portion is extended in the vehicle width direction and the arm is extended from the both end of the cross portion to the longitudinal direction of the vehicle intermediary of a curving portion. The attachments are respectively fixed to the curving portion.
Attachments to the wheels are set in the opposite end of the curving portion of the arm, intermediary of an axis. On the other hand, a tube bush portions are set in the opposite end of the curving portion of the attachments, the bush portions are rotatably attached to the axis member of the vehicle body.
The construction of the conventional torsion beam suspension will be described with reference to the drawings. As shown in FIG. 8, a torsion beam 60 includes an arm 62 and attachments 63, the arm 63 is formed by bending the ends of a straight pipe 61 to the nearly right-angle direction, the each attachment 63 is set to the end of the arm 62, and an axis 64 is set to the attachment 63. An attachment 68 is attached to a curving portion 67 between the pipe 61 and the arm part 62.
The other embodiment of the conventional torsion beam suspension will be described. As shown in FIG. 9, a torsion beam 70 includes a straight pipe 71 and attachments 72, the attachments 72 are attached to the both ends of the straight pipe 71 and the each attachment 72 is formed directing to the longitudinal direction of the vehicle and thus configures an arm 73. An axis 74 is set to the arm 73.
In the torsion beam suspension shown in FIG. 8, it is necessary that the arm 62 should be reached to the axis 64 with bending the pipe 61, so that the long pipe 61 is required, which is more expensive than a steel plate, thereby requiring the high material cost.
Further in the torsion beam suspension shown in FIG. 8, it is also necessary that the ends of the arm 62 should be closed by a cap 65 with the welding 66, as shown in FIG. 8, because the inner of the pipe goes rusty from the open ends if the arm part 62 has the open ends. Such construction unfortunately causes the high cost in manufacturing and attaching of the cap.
As to the torsion beam suspension shown in FIG. 8, it is required that the dimension between the axis 64 and the center 69a of a bush-part 69 provided in the end of the attachment 68 is exactly set as the specified dimension, however, the accuracy of bending the pipe 61 reflects that of setting the axis 64, so that the bending is required with high accuracy.
In the light of the strength of the torsion beam suspension shown in FIG. 9, the ends of the pipe 71 should be formed trapezoid or ellipse in section, or should be trimmed for forming the wrap-part 75 for the attachments 72 so that manufacturing cost of the pipe 71 becomes higher. The trimming causes the remainder of the pipe 71, thereby causing the low yield rate.
The torsion beam suspension shown in FIG. 9 requires high accuracy with setting of the attachments 72 and the wrap-part 75, because the burn through or the strength reduction of weld is caused if the clearance exists between the wrap-part 75 and the attachments 72.
The purpose of the invention is to provide a new torsion beam suspension, in which the manufacturing cost reduction and providing the good quality manufacture are achieved, in the light of the above problems.